Multiple regression analysis

Hi I was wondering if anyone can help me regarding multiple regression analysis. I have used the Stats program Minitab to analyse a large amount of data regarding the accumulation of metals by plants. I have used regression analysis to determine the effects of the concentration of the metal applied, the presence or absence of fungi and the initial location that the plants were sourced from.

I understand the output from the regression analysis and which of the factors are affecting the uptake of metals by the plants however the only thing I am having trouble explaining is the constant. The constant appears to be a significant factor in the majority of the analysis that I have undertaken. I know it has something to do with where the regression line hits the Y axis but I am not sure how to explain this. Can anyone help.

Thank you

You are correct that the constant is the y-intercept. In a nutshell, the constant is the predicted value of Y when all Xs (predictor variables) equal zero.

Hope that helps...